People not ordering food en masse would hurt small businesses the most. Plus there's a huge benefit to using an app to order food, which is why they're so popular. If the system were controlled by the restaurants and interoperable via an open API, we'd at least see some transparency.

The problem is exactly what OP stated: These things are owned by a small number of players, who can exercises control of the market from all sides. They've created a chokepoint where they can extract rents without needing to provide value in return.